mirror of
https://github.com/google/go-attestation.git
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387 lines
14 KiB
Go
387 lines
14 KiB
Go
package internal
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import (
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"bytes"
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"encoding/binary"
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"errors"
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"fmt"
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"io"
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"unicode/utf16"
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"github.com/google/certificate-transparency-go/asn1"
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"github.com/google/certificate-transparency-go/x509"
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)
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const (
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// maxNameLen is the maximum accepted byte length for a name field.
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// This value should be larger than any reasonable value.
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maxNameLen = 2048
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// maxDataLen is the maximum size in bytes of a variable data field.
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// This value should be larger than any reasonable value.
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maxDataLen = 1024 * 1024 // 1 Megabyte.
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)
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// GUIDs representing the contents of an UEFI_SIGNATURE_LIST.
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var (
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hashSHA256SigGUID = efiGUID{0xc1c41626, 0x504c, 0x4092, [8]byte{0xac, 0xa9, 0x41, 0xf9, 0x36, 0x93, 0x43, 0x28}}
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hashSHA1SigGUID = efiGUID{0x826ca512, 0xcf10, 0x4ac9, [8]byte{0xb1, 0x87, 0xbe, 0x01, 0x49, 0x66, 0x31, 0xbd}}
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hashSHA224SigGUID = efiGUID{0x0b6e5233, 0xa65c, 0x44c9, [8]byte{0x94, 0x07, 0xd9, 0xab, 0x83, 0xbf, 0xc8, 0xbd}}
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hashSHA384SigGUID = efiGUID{0xff3e5307, 0x9fd0, 0x48c9, [8]byte{0x85, 0xf1, 0x8a, 0xd5, 0x6c, 0x70, 0x1e, 0x01}}
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hashSHA512SigGUID = efiGUID{0x093e0fae, 0xa6c4, 0x4f50, [8]byte{0x9f, 0x1b, 0xd4, 0x1e, 0x2b, 0x89, 0xc1, 0x9a}}
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keyRSA2048SigGUID = efiGUID{0x3c5766e8, 0x269c, 0x4e34, [8]byte{0xaa, 0x14, 0xed, 0x77, 0x6e, 0x85, 0xb3, 0xb6}}
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certRSA2048SHA256SigGUID = efiGUID{0xe2b36190, 0x879b, 0x4a3d, [8]byte{0xad, 0x8d, 0xf2, 0xe7, 0xbb, 0xa3, 0x27, 0x84}}
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certRSA2048SHA1SigGUID = efiGUID{0x67f8444f, 0x8743, 0x48f1, [8]byte{0xa3, 0x28, 0x1e, 0xaa, 0xb8, 0x73, 0x60, 0x80}}
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certX509SigGUID = efiGUID{0xa5c059a1, 0x94e4, 0x4aa7, [8]byte{0x87, 0xb5, 0xab, 0x15, 0x5c, 0x2b, 0xf0, 0x72}}
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certHashSHA256SigGUID = efiGUID{0x3bd2a492, 0x96c0, 0x4079, [8]byte{0xb4, 0x20, 0xfc, 0xf9, 0x8e, 0xf1, 0x03, 0xed}}
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certHashSHA384SigGUID = efiGUID{0x7076876e, 0x80c2, 0x4ee6, [8]byte{0xaa, 0xd2, 0x28, 0xb3, 0x49, 0xa6, 0x86, 0x5b}}
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certHashSHA512SigGUID = efiGUID{0x446dbf63, 0x2502, 0x4cda, [8]byte{0xbc, 0xfa, 0x24, 0x65, 0xd2, 0xb0, 0xfe, 0x9d}}
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)
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// EventType describes the type of event signalled in the event log.
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type EventType uint32
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// BIOS Events (TCG PC Client Specific Implementation Specification for Conventional BIOS 1.21)
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const (
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PrebootCert EventType = 0x00000000
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PostCode EventType = 0x00000001
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unused EventType = 0x00000002
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NoAction EventType = 0x00000003
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Separator EventType = 0x00000004
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Action EventType = 0x00000005
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EventTag EventType = 0x00000006
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SCRTMContents EventType = 0x00000007
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SCRTMVersion EventType = 0x00000008
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CpuMicrocode EventType = 0x00000009
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PlatformConfigFlags EventType = 0x0000000A
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TableOfDevices EventType = 0x0000000B
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CompactHash EventType = 0x0000000C
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Ipl EventType = 0x0000000D
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IplPartitionData EventType = 0x0000000E
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NonhostCode EventType = 0x0000000F
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NonhostConfig EventType = 0x00000010
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NonhostInfo EventType = 0x00000011
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OmitBootDeviceEvents EventType = 0x00000012
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)
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// EFI Events (TCG EFI Platform Specification Version 1.22)
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const (
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EFIEventBase EventType = 0x80000000
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EFIVariableDriverConfig EventType = 0x80000001
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EFIVariableBoot EventType = 0x80000002
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EFIBootServicesApplication EventType = 0x80000003
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EFIBootServicesDriver EventType = 0x80000004
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EFIRuntimeServicesDriver EventType = 0x80000005
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EFIGPTEvent EventType = 0x80000006
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EFIAction EventType = 0x80000007
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EFIPlatformFirmwareBlob EventType = 0x80000008
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EFIHandoffTables EventType = 0x80000009
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EFIHCRTMEvent EventType = 0x80000010
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EFIVariableAuthority EventType = 0x800000e0
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)
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// ErrSigMissingGUID is returned if an EFI_SIGNATURE_DATA structure was parsed
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// successfully, however was missing the SignatureOwner GUID. This case is
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// handled specially as a workaround for a bug relating to authority events.
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var ErrSigMissingGUID = errors.New("signature data was missing owner GUID")
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var eventTypeNames = map[EventType]string{
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PrebootCert: "Preboot Cert",
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PostCode: "POST Code",
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unused: "Unused",
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NoAction: "No Action",
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Separator: "Separator",
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Action: "Action",
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EventTag: "Event Tag",
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SCRTMContents: "S-CRTM Contents",
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SCRTMVersion: "S-CRTM Version",
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CpuMicrocode: "CPU Microcode",
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PlatformConfigFlags: "Platform Config Flags",
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TableOfDevices: "Table of Devices",
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CompactHash: "Compact Hash",
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Ipl: "IPL",
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IplPartitionData: "IPL Partition Data",
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NonhostCode: "Non-Host Code",
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NonhostConfig: "Non-HostConfig",
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NonhostInfo: "Non-Host Info",
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OmitBootDeviceEvents: "Omit Boot Device Events",
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EFIEventBase: "EFI Event Base",
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EFIVariableDriverConfig: "EFI Variable Driver Config",
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EFIVariableBoot: "EFI Variable Boot",
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EFIBootServicesApplication: "EFI Boot Services Application",
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EFIBootServicesDriver: "EFI Boot Services Driver",
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EFIRuntimeServicesDriver: "EFI Runtime Services Driver",
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EFIGPTEvent: "EFI GPT Event",
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EFIAction: "EFI Action",
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EFIPlatformFirmwareBlob: "EFI Platform Firmware Blob",
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EFIVariableAuthority: "EFI Variable Authority",
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EFIHandoffTables: "EFI Handoff Tables",
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EFIHCRTMEvent: "EFI H-CRTM Event",
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}
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func (e EventType) String() string {
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if s, ok := eventTypeNames[e]; ok {
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return s
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}
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return fmt.Sprintf("EventType(0x%x)", uint32(e))
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}
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// UntrustedParseEventType returns the event type indicated by
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// the provided value.
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func UntrustedParseEventType(et uint32) (EventType, error) {
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// "The value associated with a UEFI specific platform event type MUST be in
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// the range between 0x80000000 and 0x800000FF, inclusive."
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if (et < 0x80000000 && et > 0x800000FF) || (et < 0x0 && et > 0x12) {
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return EventType(0), fmt.Errorf("event type not between [0x0, 0x12] or [0x80000000, 0x800000FF]: got %#x", et)
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}
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if _, ok := eventTypeNames[EventType(et)]; !ok {
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return EventType(0), fmt.Errorf("unknown event type %#x", et)
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}
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return EventType(et), nil
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}
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// efiGUID represents the EFI_GUID type.
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// See section "2.3.1 Data Types" in the specification for more information.
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// type efiGUID [16]byte
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type efiGUID struct {
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Data1 uint32
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Data2 uint16
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Data3 uint16
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Data4 [8]byte
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}
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func (d efiGUID) String() string {
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var u [8]byte
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binary.BigEndian.PutUint32(u[:4], d.Data1)
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binary.BigEndian.PutUint16(u[4:6], d.Data2)
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binary.BigEndian.PutUint16(u[6:8], d.Data3)
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return fmt.Sprintf("%x-%x-%x-%x-%x", u[:4], u[4:6], u[6:8], d.Data4[:2], d.Data4[2:])
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}
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// UEFIVariableDataHeader represents the leading fixed-size fields
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// within UEFI_VARIABLE_DATA.
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type UEFIVariableDataHeader struct {
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VariableName efiGUID
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UnicodeNameLength uint64 // uintN
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VariableDataLength uint64 // uintN
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}
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// UEFIVariableData represents the UEFI_VARIABLE_DATA structure.
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type UEFIVariableData struct {
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Header UEFIVariableDataHeader
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UnicodeName []uint16
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VariableData []byte // []int8
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}
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// ParseUEFIVariableData parses the data section of an event structured as
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// a UEFI variable.
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//
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// https://trustedcomputinggroup.org/wp-content/uploads/TCG_PCClient_Specific_Platform_Profile_for_TPM_2p0_1p04_PUBLIC.pdf#page=100
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func ParseUEFIVariableData(r io.Reader) (ret UEFIVariableData, err error) {
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err = binary.Read(r, binary.LittleEndian, &ret.Header)
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if err != nil {
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return
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}
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if ret.Header.UnicodeNameLength > maxNameLen {
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return UEFIVariableData{}, fmt.Errorf("unicode name too long: %d > %d", ret.Header.UnicodeNameLength, maxNameLen)
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}
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ret.UnicodeName = make([]uint16, ret.Header.UnicodeNameLength)
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for i := 0; uint64(i) < ret.Header.UnicodeNameLength; i++ {
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err = binary.Read(r, binary.LittleEndian, &ret.UnicodeName[i])
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if err != nil {
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return
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}
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}
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if ret.Header.VariableDataLength > maxDataLen {
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return UEFIVariableData{}, fmt.Errorf("variable data too long: %d > %d", ret.Header.VariableDataLength, maxDataLen)
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}
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ret.VariableData = make([]byte, ret.Header.VariableDataLength)
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_, err = io.ReadFull(r, ret.VariableData)
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return
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}
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func (v *UEFIVariableData) VarName() string {
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return string(utf16.Decode(v.UnicodeName))
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}
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func (v *UEFIVariableData) SignatureData() (certs []x509.Certificate, hashes [][]byte, err error) {
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return parseEfiSignatureList(v.VariableData)
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}
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// UEFIVariableAuthority describes the contents of a UEFI variable authority
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// event.
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type UEFIVariableAuthority struct {
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Certs []x509.Certificate
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}
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// ParseUEFIVariableAuthority parses the data section of an event structured as
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// a UEFI variable authority.
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//
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// https://uefi.org/sites/default/files/resources/UEFI_Spec_2_8_final.pdf#page=1789
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func ParseUEFIVariableAuthority(r io.Reader) (UEFIVariableAuthority, error) {
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v, err := ParseUEFIVariableData(r)
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if err != nil {
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return UEFIVariableAuthority{}, err
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}
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certs, err := parseEfiSignature(v.VariableData)
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return UEFIVariableAuthority{Certs: certs}, err
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}
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// efiSignatureData represents the EFI_SIGNATURE_DATA type.
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// See section "31.4.1 Signature Database" in the specification for more information.
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type efiSignatureData struct {
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SignatureOwner efiGUID
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SignatureData []byte // []int8
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}
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// efiSignatureList represents the EFI_SIGNATURE_LIST type.
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// See section "31.4.1 Signature Database" in the specification for more information.
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type efiSignatureListHeader struct {
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SignatureType efiGUID
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SignatureListSize uint32
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SignatureHeaderSize uint32
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SignatureSize uint32
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}
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type efiSignatureList struct {
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Header efiSignatureListHeader
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SignatureData []byte
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Signatures []byte
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}
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// parseEfiSignatureList parses a EFI_SIGNATURE_LIST structure.
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// The structure and related GUIDs are defined at:
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// https://uefi.org/sites/default/files/resources/UEFI_Spec_2_8_final.pdf#page=1790
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func parseEfiSignatureList(b []byte) ([]x509.Certificate, [][]byte, error) {
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if len(b) < 28 {
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// Being passed an empty signature list here appears to be valid
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return nil, nil, nil
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}
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signatures := efiSignatureList{}
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buf := bytes.NewReader(b)
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certificates := []x509.Certificate{}
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hashes := [][]byte{}
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for buf.Len() > 0 {
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err := binary.Read(buf, binary.LittleEndian, &signatures.Header)
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if err != nil {
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return nil, nil, err
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}
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if signatures.Header.SignatureHeaderSize > maxDataLen {
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return nil, nil, fmt.Errorf("signature header too large: %d > %d", signatures.Header.SignatureHeaderSize, maxDataLen)
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}
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if signatures.Header.SignatureListSize > maxDataLen {
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return nil, nil, fmt.Errorf("signature list too large: %d > %d", signatures.Header.SignatureListSize, maxDataLen)
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}
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signatureType := signatures.Header.SignatureType
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switch signatureType {
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case certX509SigGUID: // X509 certificate
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for sigOffset := 0; uint32(sigOffset) < signatures.Header.SignatureListSize-28; {
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signature := efiSignatureData{}
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signature.SignatureData = make([]byte, signatures.Header.SignatureSize-16)
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err := binary.Read(buf, binary.LittleEndian, &signature.SignatureOwner)
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if err != nil {
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return nil, nil, err
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}
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err = binary.Read(buf, binary.LittleEndian, &signature.SignatureData)
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if err != nil {
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return nil, nil, err
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}
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cert, err := x509.ParseCertificate(signature.SignatureData)
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if err != nil {
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return nil, nil, err
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}
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sigOffset += int(signatures.Header.SignatureSize)
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certificates = append(certificates, *cert)
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}
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case hashSHA256SigGUID: // SHA256
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for sigOffset := 0; uint32(sigOffset) < signatures.Header.SignatureListSize-28; {
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signature := efiSignatureData{}
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signature.SignatureData = make([]byte, signatures.Header.SignatureSize-16)
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err := binary.Read(buf, binary.LittleEndian, &signature.SignatureOwner)
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if err != nil {
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return nil, nil, err
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}
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err = binary.Read(buf, binary.LittleEndian, &signature.SignatureData)
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if err != nil {
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return nil, nil, err
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}
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hashes = append(hashes, signature.SignatureData)
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sigOffset += int(signatures.Header.SignatureSize)
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}
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case keyRSA2048SigGUID:
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err = errors.New("unhandled RSA2048 key")
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case certRSA2048SHA256SigGUID:
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err = errors.New("unhandled RSA2048-SHA256 key")
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case hashSHA1SigGUID:
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err = errors.New("unhandled SHA1 hash")
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case certRSA2048SHA1SigGUID:
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err = errors.New("unhandled RSA2048-SHA1 key")
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case hashSHA224SigGUID:
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err = errors.New("unhandled SHA224 hash")
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case hashSHA384SigGUID:
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err = errors.New("unhandled SHA384 hash")
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case hashSHA512SigGUID:
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err = errors.New("unhandled SHA512 hash")
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case certHashSHA256SigGUID:
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err = errors.New("unhandled X509-SHA256 hash metadata")
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case certHashSHA384SigGUID:
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err = errors.New("unhandled X509-SHA384 hash metadata")
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case certHashSHA512SigGUID:
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err = errors.New("unhandled X509-SHA512 hash metadata")
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default:
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err = fmt.Errorf("unhandled signature type %s", signatureType)
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}
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if err != nil {
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return nil, nil, err
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}
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}
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return certificates, hashes, nil
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}
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// EFISignatureData represents the EFI_SIGNATURE_DATA type.
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// See section "31.4.1 Signature Database" in the specification
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// for more information.
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type EFISignatureData struct {
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SignatureOwner efiGUID
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SignatureData []byte // []int8
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}
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func parseEfiSignature(b []byte) ([]x509.Certificate, error) {
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certificates := []x509.Certificate{}
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if len(b) < 16 {
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return nil, fmt.Errorf("invalid signature: buffer smaller than header (%d < %d)", len(b), 16)
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}
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buf := bytes.NewReader(b)
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signature := EFISignatureData{}
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signature.SignatureData = make([]byte, len(b)-16)
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if err := binary.Read(buf, binary.LittleEndian, &signature.SignatureOwner); err != nil {
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return certificates, err
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}
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if err := binary.Read(buf, binary.LittleEndian, &signature.SignatureData); err != nil {
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return certificates, err
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}
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cert, err := x509.ParseCertificate(signature.SignatureData)
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if err == nil {
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certificates = append(certificates, *cert)
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} else {
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// A bug in shim may cause an event to be missing the SignatureOwner GUID.
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// We handle this, but signal back to the caller using ErrSigMissingGUID.
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if _, isStructuralErr := err.(asn1.StructuralError); isStructuralErr {
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var err2 error
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cert, err2 = x509.ParseCertificate(b)
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if err2 == nil {
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certificates = append(certificates, *cert)
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err = ErrSigMissingGUID
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}
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}
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}
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return certificates, err
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}
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